Senate Homeland Security and Governmental Affairs Committee Chairman Sen. Joseph Lieberman, I-Conn, listens as the committee's ranking Republican, Sen. Susan Collins, R-Maine, speaks during the committee's hearing in May on the investigation into the U.S. Secret Service prostitute scandal.

A federal watchdog told lawmakers Friday that six women who met with U.S. Secret Service employees in Colombia in April were paid for sex and that other Defense Department and White House personnel might have been involved.

Charles K. Edwards, acting inspector general for the Department of Homeland Security, shared initial findings of his months-long investigation with Congress on Friday, despite saying that his final investigative report will not be released publicly, pursuant to department policy. Edwards said he is in the final stages of the investigation.

But Sen. Susan Collins, R-Maine, one of several lawmakers who requested the probe, said the inconclusiveness surrounding possible White House involvement still troubles her.

“The White House explicitly denied any involvement after its own investigation, and now the IG is questioning that account,” Collins said Friday. “This raises concerns about the credibility of the White House investigation.”

Edwards said his investigation included interviews with 251 Secret Service employees and a review of travel records, hotel registries and U.S. Embassy cables. He launched the probe at the request of lawmakers in late May.

In a letter to House and Senate committees, Edwards said that 13 agency staffers “had personal encounters” with women at two Cartagena hotels and a private residence after meeting them at nightclubs in mid-April. Three of the women left without asking for money, five asked for money and were paid, four were refused payment and one woman was paid only after she summoned a Colombian police officer, according to investigators.

The payment dispute that unfolded in the early hours of April 12, just hours before President Barack Obama arrived in Cartagena for the Summit of the Americas, exposed the misconduct to local authorities and set off one of the most embarrassing episodes in Secret Service history.

Eight Secret Service employees, including two senior supervisors, eventually lost their jobs, but two of them are fighting to be reinstated. Three others were cleared of serious misconduct.

Seven soldiers and two Marines also were implicated in the scandal and received administrative punishments. Three of those personnel requested courts-martial.

Allaying one of the primary concerns of lawmakers, Edwards said he found no evidence that the misconduct “compromised the safety and security of the president or any sensitive information.”

But a hotel registry reviewed by investigators suggested that two other U.S. government employees — working for the Defense Department and White House Communication Agency — “may have had contact with foreign nationals,” Edwards said. Investigators did not pursue the individuals because the Homeland Security inspector general lacks the authority to investigate non-DHS personnel.

Secret Service spokesman Ed Donovan said the agency had no initial comment on the investigation.